Even in highly centralised parties such as the DUP and Sinn Fein, candidate selections have the potential to create bitter in-fighting.
In more open parties such as the UUP and SDLP, selections are even more hazardous.
But the UUP’s selection process has been remarkably smooth up until now.
Nine candidates put their names forward to replace Tom Elliott and Danny Kinahan as MLAs and there appeared to have been a clean contest, with none of the acrimonious negative briefing which can accompany the chance to get a £48,000-a-year job.
The local association meetings which narrowed the choice down to two candidates for each seat passed without incident.
But the final decision between those candidates has left some within the party unhappy.
In South Antrim, the choice of Adrian Watson to replace Mr Kinahan shows the difficulty for Mike Nesbitt in defining what the UUP stands for.
To many people, Mr Watson would seem to be politically closer to the Rev William McCrea, who lost to Mr Kinahan, than to the moderate, castle-dwelling, socially-liberal new MP.
Referring to the choice of Mr Watson one UUP member said that Mr Watson was the “direct opposite” of his predecessor. In that sense, the party will now be slightly more like the DUP in the Assembly.
Meanwhile, the extraordinary gaffe in Fermanagh-South Tyrone where votes were apparently miscounted has left some local party members deeply unhappy.
Some party sources had wanted Neil Somerville to be selected as he is from the Tyrone end of the constituency, which may help it unseat the DUP’s Lord Morrow, thus securing a second Assembly seat.
But the manner of his selection ahead of victims’ campaigner Kenny Donaldson – the clear choice of the local association – has created fissures.